Electromagnetic switch with canted contacts



Nov. 29, 1966 o. M. ULBING ELECTROMAGNETIC SWITCH WITH CANTED CONTACTS 5 Sheets-Sheet 1 Filed Feb. 1, 1963 Nov. 29', 1966 o. M. ULBING ELECTROMAGNETIC SWITCH WITH CANTED CONTACTS Filed Feb. 1, 1963 5 Sheets-$heet 2 0 44/9/55. Z/AB/A/G INVENTOR ATTORNEY Nov. 29, 1966 O. M. ULBING ELECTROMAGNETIC SWITCH WITH CANTED CONTACTS Filed Feb. 1, 1963 5 Sheets-Sheet 3 pi FIG.3d

arm/96 M. UAE/A/G INVENTOR ATTORNEY United States Patent i 3,289,132 ELECTROMAGNETIC SWITCH WITH CANTED CONTACTS Otrnar M. Ulbing, Johnson City, N.Y., assignor, by direct and mesne assignments, of fifty percent to Robert S. Rinehuls, Ringharnton, N.Y., and twenty-five percent to Richard Rinehuls, Port Crane, N.Y.

Filed Feb. 1, 1963, Ser. No. 255,578 12 Claims. (Cl. 335-189) This invention relates to electric switches, and more particularly to an improved electromagnetic relay having a novel contact configuration which operates to make relatively bouncefree contact, to maintain good electrical contact and to facilitate easy connection and disconnection of the relay. The improved relay, though not limited thereto, is particularly suitable for use in electrical data processing or business machines. In many such machines it is frequently necessary or desirable to connect groups of electrical wires to respective electrical relays in such a manner that they may be disconnected easily at will 'for maintenance, testing and various other purposes. In the interests of miniaturization, or at least economical use of the space in such equipment, it is desirable that such relays be mounted either close together, or close to walls, structures and to other components in such equipment. Very many relays of the prior art are so constructed that access to the relay terminals is made extremely difficult or impossible if the relays are mounted close together or close to other devices. The present invention incorporates an improved contact and terminal configuration arranged to provide easy access to any of the many terminals of a multi-terminal relay. Thus it is one object of the present invention to provide an improved electromagnetic relay which allows easy access to all of its terminals.

In such equipment it also is frequently desirable that all wire connections to a given multi-contact relay be routed to the relay from the same direction, so that cabling or wiring associated with a given relay lies on one side of the relay, thereby facilitating mounting the relay close to a closed wall or panel or other component, and thereby also facilitating connection and disconnection of the relay. Thus it is another object of the invention to provide an improved relay to which all connections may be made from the same side, so that conductors leading to the relay all may be led in the same direction to and from the relay.

Most business machines receive only periodic maintenance, and hence it is desirable that the relays used in such machines be as foolproof and reliable as possible. A most frequent limitation of electromagnetic relays in general is their allowable number of cycles, i.e., openings and closings of their contacts, before the contacts become pitted or corroded or dirty enough to fail. Much effort has been directed toward the use of special contact metals to avoid pitting and corrosion. The contact arrangement of the present invention provides an improved automatic contact wiping action each time a :pair of contacts are opened and closed, thereby markedly increasing useful contact life. Thus it is a further, and very important object of the present invention to provide an improved relay in which the contacts have an automatic wiping action which results in contact cleaning.

When a relay electromagnet is energized, it translates one or more movable contacts into physical engagement and electrical contact with one or more stationary contacts. Relay operating coil current is usually made adequate to insure that the force with which the movable contact is urged against the stationary contact is sufficient to positively connect the two electrically, and to hold the two fairly tightly together, so that machine vibrations and Patented Nov. 29, 1966 the like do not materially increase contact resistance. It frequently happens that the coil force necessary to .provide positive closing and to prevent subsequent chattering, is sufficient to cause contact bounce when the relay closes, particularly if either or both of a pair of mating contacts vare resiliently mounted, and mounting with some degree of resiliency is almost always necessary in order to insure contact closing in the presence of inevitable contact wear. Contact bounce tends to cause arcing, aggravating contact wear, and in some circuits causes electrical noise which may interfere with proper machine operation. The contact arrangement of the present invention decreases the probability of contact bounce, thereby insuring larger contact life and more accurate and noisefree switching. Thus it is a further object of the present invention to provide an improved relay having less tendency for contact bounce or chatter. While the invention was originally conceived and constructed in connection with an electromagnetic-operated switch, or relay, it will become apparent as the description proceeds, that the invention also will be useful in a variety of other switch assemblies where switch contact arms are translated by a variety of other actuating devices.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is a side view of one form of electromagnetic relay constructed in accordance with the invention;

FIG. 2 is an end view of the relay of FIG. 1;

FIG. 3 is a top view of the relay of FIG. 1;

FIG. 4 is an isometric view looking generally at the bottom of the relay,

FIG. 5 is an isometric view looking generally at the top and side of the relay, and

FIG. 6 is a detail view in disassembled form illustrating in detail the hinge operation of the relay of FIGS. 1-5.

FIG. 7 is a plan view diagram illustrating three relays of the present invention mounted within a housing for the purpose of illustrating the improved accessibility of the relay terminals of the present invention;

FIGS. 8a and 8b are diagrams illustrating details of the contact action of prior art relays and the present relays, respectively.

FIGS. and 8d illustrate the construction and operation of a modified form of contact wherein the width of a leaf spring carrying a contact is arranged in the direction of the resultant bounce force, thereby to minimize contact bounce.

Referring now to the figures, the relay of the present invention is shown as including a substantially U-shaped magnetic soft iron frame member 12 having an upper portion 14, a middle portion 16 and a lower portion 18. Screw 20 passes through a hole in mounting bracket 22 and through middle portion 16 of frame member 12, threading into magnetic core member 24, thereby rigidly affixing frame member 12 and core 24 to mounting bracket 22. Holes 26, 26 are provided in bracket 22 to allow mounting of the entire assembly at a desired location on an electrical chassis or other machine part. Lower arm 18 of frame member 12 is fastened .by means of rivets or screws (not shown) to terminal block 50, which is formed of insulating material and which carries a plurality of terminal bars 51-59 which, as will be explained below, are located in block 50 in a special arrangement. Each terminal bar may be made conveniently from flat strap stock, and the terminal bars may be cast in place if cast forms of terminal blocks are utilized. The lower end of each terminal bar is provided with a threaded hole, as best seen in FIG. 4, and screws (not shown) threaded in the holes may be used to attach one or more external wires to each terminal bar. The upper ends of terminal bars 51-59 are connected variously to the relay operating coil 31 and to movable and stationary contacts of the relay.

Upper arm 14 of frame member 12 terminates in a yoke type and against which the relay armature assem- 'bly is pivotably mounted, as best seen in FIG. 6.

Armature 30 rests against faces 15, 15 of the end of arm 14 of the frame, and is pivoted around an axis X-X defined by faces 15, 15 as the relay is energized and deenergized. Projections 17, 17 on the end of arm 14 register in slots 11, 11 in the armature to prevent sidewise motion of the armature. Spring anchor bar 19 rigidly fastened on arm 14 serves to anchor one end of tension spring 28, and the other end of spring 28 is connected at 29 to one end of armature 30, as best seen in FIG. 5, thereby tending to pull the upper end of armature 30 leftwardly as viewed in FIG. 1. Tongue end 41 of spring anchor bar 19 protrudes through slot 42 in armature 30, to prevent the armature assembly from falling free when the tension in spring 28 is being adjusted or when spring 28 is being changed. The precise manner in which the relay armature is mounted for pivotal movement is not a feature of the present invention, and a variety of equivalent pivotal mountings may be substituted without departing from the invention.

Armature 30, preferably made of soft iron, is fixedly attached to and carries a movable insulating contact arm carrying member 35. As best seen in FIG. where much of insulating member 35 is cut away, screw 34 fastens insulating member 35 to armature 30, screw 34 being threaded into armature 30 at 36. Member 35 carries a plurality of movable contact arms, two (38, 39) being shown in the specific disclosed embodiment. Contact arms comprise flexible leaf-spring type contact arms preferably made of Phosphor bronze or the like. The upper ends of arms 38, 39 are riveted to insulating member 35, and a wire connection is made from each of the arms to a respective terminal bar located in insulating terminal block 50. For example, one end of wire 49 is soldered to the rivet which secures the upper end of contact arm 38, and the other end of wire 40 is soldered to terminal bar 51 located in terminal block 50, as shown in FIG. 1. Wire 41 (FIG. 4) similarly connects arm 39 to terminal 'bar 52. It should be noted that the planes of leaf-spring contact arms 38, 39 are canted with respect to axis X-X and with respect to the direction of motion of armature 30, for purposes which will 'be explained below in detail.

Magnetic operating coil 31 surrounds core 24, and the ends of the winding of coil 31 are connected to the upper ends of terminal bars 53 and 54. In the absence of current through operating coil 31, tension spring 28 urges the upper end of armature 30 leftwardly as viewed in FIG. 1, thereby urging the lower ends of movable contact arms 38, 39 rightwardly, so that contact tips 38' and 39' make electrical contact with contact tips 55, 56 of sta tionary terminal bars 55, 56 carried in terminal block 50. When operating current is connected through terminal bars 53, 54 and the winding of coil 31, core 24 attracts armature 3t), pivoting it about axis X-X against the force of spring 28, thereby disconnecting movable arms 38, 39 from contacts 55, 56 and connecting them to stationary contacts 57, 58, respectively. Upon subsequent de-energization of coil 31, contact arms 38, 39 are returning by spring 28 to their original positions.

As will be particularly evident from FIGS. 2 and 4, the terminal bars 51-59 are not arranged in two parallel rows, as is usual in the prior art, but instead arranged substantially in a V configuration, with the contacts (53, 54) nearest the rear of the relay considerably closer to the centerline of terminal block 50 than the contacts (55, 56) nearest the front of the relay, the latter being spread much further apart. It is also important to note that the planes of the contact terminal bars 5159 are not parallel to (or perpendicular to) the pivot axis X-X of the relay or the direction of translation Y-Y of the lower ends of movable arms 38, 39, as is usual in the prior art, but instead canted with respect thereto. The location of each terminal at a distance from the relay centerline which is roughly proportional to its distance from the rear of the relay, so that front terminals are further from the relay centerline than rear terminals, together with the canting of the planes of the terminal bars, serves to provide remarkably easy access to all relay terminals, all from the same direction.

In FIG. 7 the undersides of three relays constructed in accordance with the invention are shown, with the three relays mounted within a housing 70. It will be seen that all of the terminals of all three relays may be operated on with a screwdriver from front side 70a of housing 70. Since access to all relay terminals may be had from one side, the relays may be mounted close to or against rear wall 7% and side walls 7tlc, 70d, with a considerable savings in space. The wires of cables 71, 72 and 73 may be connected to respective of the relays, with the screws of the terminal bars passing through eyelet terminals of the type shown at 75, for example, or yoke terminals of the type shown at 76, to fasten the individual wires of the cables to individual relay terminals. It will be seen that each screw will face substantially toward the front center section of its associated terminal block, providing easy screwdriver access.

FIGS. 8a and 8b contrast contact-making action of prior art relay contacts with those of the invention. The center, or movable contact in each figure may be assumed to be mounted on a somewhat flexible movable contact arm (not shown) fastened to an armature (not shown) the latter being urged in one direction by a spring and in the opposite direction by an electromagnet. In each of these figures, axis X-X represents the relay pivot axis. As the armature of the usual prior art relay moves, in the directions indicated by arrows Y, Y in FIG. 8a, movable contact translates between stationary contacts 81 and 82, and it will be seen that the same portions of the movable contact always touch the same portions of the stationary contacts, so that arcing always tends to occur at the same portions of the contact tips. In FIG. 8b, axis X-X also represents the relay pivot axis, and arrows YY represent the direction in which canted movable contact 80 is translated when the armature moves. It will be seen that because stationary contacts 81' and 82' are displaced from the YY axis and canted as shown, that a lateral force component is developed as movable contact 80 touches either stationary con-tact. For example, as the flexible contact arm carrying movable contact 80 urges contact 80 against stationary contact 81', the canting of the contacts urges contact 80 slightly right wardly as viewed in FIG. 8b, providing a wiping action. Conversely, .when movable contact 80' is urged against stationary contact 82, the lateral force component developed due to the canting of the contacts will be seen to urge movable contact 80' leftwardly. It will be seen that energization of relay coil 31 to urge arms 38 and 39 against the contacts of terminal bars 57 and 58, respectively tends to urge the lower ends of arms 38 and 39 toward each other, while the action of spring 2 8 when coil 31 is not energized urging arms 38 and 39 against the contacts of terminal bars 55 and 56, respectively tends to urge the lower ends of arms 38 and 39 farther apart. It will be apparent that a converse arrangement can be adopted in some applications of the invention, whereby energization will result in contact arms being urged apart and spring action will result in contact arms being urged together, without departing from the invention. The contact wiping provided by these laterally-acting forces has proven to considerably increase contact life. While FIG. 8b illustrates a single movable contact, which would provide a force on the armature in a single lateral direction, it will be clear from FIGS. 1-6 that in the relay shown, that the reaction force on the armature resulting from the lateral force which urges movable arm 38 in one lateral direction will be opposed by a substantially equal reaction force in the opposite direction from arm 39, and hence the lateral forces do not tend to cause the relay armature assembly to bind.

It also should be noted that then movable contact 80 in FIG. 8a is suddenly urged against contact 81 or 82, that the entire opposing forces developed by the resiliency of the mountings of either or both contacts will act exactly along axis YY, and tend to oppose the armature actuating force, so that the contact may bounce. It is possible, of course, in a relay to provide rigid contact mountings to decrease such resilient effects, but a certain amount of resilience is usually deemed mandatory to compensate for contact wear. In FIG. 8b the canting of the contacts causes a portion or component of the resilient force to be expended laterally, thereby decreasing resilient force opposition to the armature actuating force and considerably decreasing or eliminating the amount of contact bounce for a relay with a given amount of resilience in its contact mountings, so that the contacts of the invention tend to close in a more positive and certain manner.

The lateral component of the resilient bounce force, and the remaining longitudinal component of the bounce force, combine vectorially into a resultant bounce force. The longitudinal bounce force will depend upon the armature force and contact arm resiliency. The lateral component will depend upon armature force and the angle between the planes of the mating contacts and the armature direction of motion. In FIG. 80 the lateral component, the longitudinal component, and the resultant bounce force when contact 80 strikes contact 81' are indicated by vectors P F and F If one or both of a pair of resilient spring arms are so arranged that their widths extend in the direction of the resultant bounce force F contact bounce will be minimized. For example, assuming that contacts 81' and 82' in FIG. 8c are rigidly mounted and that contact 80' is carried on a resilient leafspring type of contact arm, if the plane or width of the resilient contact arm is made to extend substantially in the direction of the resultant bounce force, and only the end of the arm is twisted to provide a contact relationship such as that shown in FIGS. 8b and 8c, contact bounce will be minimized, since the contact arm will be essentially rigid in the direction of the resultant bounce force, i.e., about its width. In FIGS. 8c and 8d, the width of the resilient contact arm extends in the direction of resultant force F at an angle 0 to the direction of motion Y--Y of the armature (not shown) which translates the resilient arm and contact 80', and only the contact 80' end of the arm is twisted to provide a contact mating relationship such as shown in FIGS. 8]; and 80. As well as minimizing contact bounce, establishing the resilient contact arm plane in the direction shown will be seen to improve contact wipi-ng action, since the forces lateral to armature direction of motion now will act more perpendicularly to the width of the contact arm, more nearly about the principal bending axis of the arm. It will be apparent that the technique illustrated in FIGS. 80 and 8d may be applied to stationary contact arms as well as to movable contact arms.

While the specific embodiment disclosed in detail illustrates the use of semi fiexible movable con-tact arms and essentially rigidly mounted stationary contacts, it should be noted that a reverse arrangement may be used without departing from the invention, in which the stationary contacts are carried on semi-flexible terminal bars and the movable contacts are essentially rigidly connected to the movable armature, and further, a compromise arrange ment may be used, in which both the stationary and the movable contacts are carried on semi-flexible arms, all within the spirit of the teachings of the present invention.

I claim:

1. An electromagnetic switch, comprising, in combination: a base structure; a pair of stationary contacts mounted on said base structure and spaced apart at the ends of an arcuate path, each of said stationary con-tacts having a contact surface area the plane of which intersects the plane of said arcuate path substantially non-perpendicularly; a flexible contact arm mounted on said base structure to pivot between said stationary contacts about an axis situated substantially at the center of curvature of said arcuate path, said contact arm having a pair of contact surface areas on opposite sides of said contact arm, the planes of which are arranged substantially non-perpendicularly to the plane of said arcuate path; and elect-romagnet means mounted on said base structure in driving relation-ship to said arm to pivot said flexible contact arm and urge one of said contact surface areas of said contact arm against the contact surface area of one of said stationary contacts.

2. An electromagnetic switch, comprising, in combination: a base structure; a pair of stationary contacts mounted on said base structure and spaced apart at the ends of an arcuate path; a movable contact arm having a movable contact, said contact arm being pivotally mounted on said base structure to reciprocate along said path; el-ectromagnet means mounted on said base structure and operable to urge said movable contact in one direction along said path; and spring means mechanically connected between said contact arm and said base structure to urge said movable contact in an opposite direction along said path, each of said stationary contacts having a contact surface area the plane of which non-perpendicularly intersects the plane of said path, said movable contact having firs-t and second contact areas adapted to engage said contact surface areas of said stationary contacts.

3. An electromagnetic switch, comprising, in combination: a pair of stationary contacts spaced apart on opposite sides of a reference plane, each of said contacts having a contact surface area, the plane of each contact surface area being disposed non-parallel to each other and to said reference plane; a pair of resilient movable contact arms, one end of each movable contact arm being mechanically fastened to a movable insulating member and the other end of each movable contact arm having a contact surface area adapted upon translation of said movable insulating member to engage a respective one of said contact surface areas of said stationary contacts, the planes of said contact surface areas of said movable contact arms being canted to be parallel upon engagement to the planes of said contact surface areas of said stationary contacts; and means for pivoting said movable insulating member about an axis perpendicular to said reference plane to engage and disengage said respective stationary and movable contact surface area.

4. Apparatus according to claim 3 in which said means for pivoting said movable insulating member comprises an electromagnet, a magnetic member mechanically attached to said movable insulating member to be attracted by said electromagnet to pivot said movable insulating member about said axis in a first direction, and spring means connected to urge said movable insulating member about said axis in a second direction opposite to said first direction.

5. Apparatus according to claim 3 in which said contact surface areas on opposite sides of said reference plane are canted in opposite directions with respect to said reference plane, whereby the lateral reaction forces upon said movable insulating member resulting from urging the movable contact on one side of said reference plane against the stationary contact on said one side of said reference plane are substantially cancelled by the lateral reaction forces resulting from urging the other movable contact against the other stationary contact.

6. A switch assembly, comprising, in combination: a stationary contact arm having a first contact surface area; a pivoting resilient contact arm having a second contact surface area; and means for moving said movable contact arm in a direction parallel to a reference plane to cause said second contact surface area to reciprocate along an arcuate path parallel to said reference plane to engage and disengage said first contact surface area, said first and second contact surface areas being arranged to be substantially parallel to each other upon engagement and nonperpendicular upon engagement to said path and said reference plane, whereby urging said second contact surface area against said first contact surface area results in a component of force perpendicular to said reference plane causing relative movement between said contact surface areas in a direction parallel to the planes of said contact surface areas.

7. An assembly according to claim 6 in which a least one of said contact arms includes a spring portion having a first degree of stiffness in a first direction and substantially more stiffness in a second direction, and in which said spring portion is oriented so that said second direction substantially coincides with the resultant of said lateral component of force and the reaction force acting parallel to said reference plane upon engagement of said contact surface areas.

8. An assembly according to claim 6 in which at least one of said contact arms comprises a leaf spring having a substantial portion of its width oriented parallel to the resultant of forces acting upon said first contact surface area upon engagement of said first and second contact surface areas.

9. An electrical switch assembly comprising, in combination: a fixed contact means having a first contact surface area; a movable contact means having a second contact surface area; means for translating said movable contact means along a predetermined path to engage and disengage said contact surface areas, at least one of said contact means being resilient; said first contact surface area being non-perpendicularly arranged with respect to said path, whereby translating said movable contact means against said stationary contact means provides a resilient reaction force in a second direction angularly displaced from said path, at least one of said contact means including a flat spring portion having its width oriented substantially in the direction of said resilient reaction force.

10. An assembly according to claim 6 in which said movable contact arm is pivotally mounted to pivot about an axis perpendicular to the reference plane, and in which said means for moving said movable contact arm comprises electromagnetic means for pivoting said movable contact arm about said axis in one direction and spring means connected to urge said movable contact arm about said axis in a second direction opposite to said one direction.

11. An electromagnet switch assembly, comprising, in combination: a terminal block member; a plurality of terminal bars extending through said terminal block member and spaced at lateral distances from a reference plane which vary in accordance with their respective distances from one edge of said terminal block member, the plane of each of said terminal bars being obliquely oriented with respect to said reference plane; a movable armature 6 pivotally mounted on one side of said terminal block member to pivot about an axis perpendicular to said reference plane; an electromagnet coil mounted on said one side of said terminal block member to pivot said armature; .a plurality of movable contact arms mounted on said movable armature, each of movable contact arms and a group of said terminal bars having a contact surface area, the planes of each of said contact surface areas being oblique to said reference plane, the end of each terminal bar on the side of said terminal block member opposite from said one side having means for attaching an external connecting conductor, and the other end of each of said terminal bars being electrically connected variously to said coil and said contact surface areas.

12. An electromagnet switch assembly, comprising, in combination: a terminal block member having a front end and a reference plane passing through said terminal block member; a plurality of terminal bars projecting from one side of said terminal block member, comprising a first group of terminal bars mounted on one side of said reference plane and a second group of terminal bars mounted on the other side of said reference plane, each of said terminal bars having a front surface portion and a connection means disposed on said front surface portion, said front surface portions of said bars being obliquely oriented with respect to said reference plane to face said front end of said terminal block member; a movable armature pivotally mounted on said terminal block member on a second side opposite said one side, said armature being pivotable about an axis perpendicular to said reference plane; an electromagnet coil mounted on said second side of said terminal block member to pivot said armature in a first direction about said axis; spring means mounted on said second side to pivot said armature in a second direction about said axis; a plurality of movable contact arms mounted on said armature, each of said contact arms having a surface area, the planes of said surface areas each being arranged oblique to said reference plane; a plurality of fixed contacts mounted on said second side of said terminal block member to be engaged by said surface areas of said movable contact arms, each of said fixed contacts having contact surface areas canted with respect to said reference plane to be parallel upon engagement with respective of said surface areas of said movable contact arms.

References Cited by the Examiner UNITED STATES PATENTS 1,791,123 2/1931 Da Costa 174-59 1,945,561 2/1934 Norviel 174-60 2,329,036 9/1943 Ebert 200-87 2,497,306 2/ 1950 Landmeier 200-164 2,716,682 8/ 1955 Franklin 200-164 2,811,617 10/1959 Townsend 200-166 2,924,685 2/1960 Burch 200-166 2,958,066 10/1960 Humphrey 339-198 3,145,279 8/1964 Vradenburgh 200-164 3,185,757 5/1965 Phillips 174-45 FOREIGN PATENTS 915,333 1/1963 Great Britain.

OTHER REFERENCES German application 1,042,067, Oct. 20, 1958.

BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

B. DOBECK, J. J. BAKER, Assistant Examiner. 

1. AN ELECTROMAGNETIC SWITCH, COMPRISING, IN COMBINATION: A BASE STRUCTURE; A PAIR OF STATIONARY CONTACTS MOUNTED ON SAID BASE STRUCTURE AND SPACED APART AT THE ENDS OF AN ARCUATE PATH, EACH OF SAID STATIONARY CONTACTS HAVING A CONTACT SURFACE AREA THE PLANE OF WHICH INTERSECTS THE PLANE OF SAID ARCUATE PATH SUBSTANTIALLY NON-PERPENDICULARLY; A FLEXIBLE CONTACT ARM MOUNTED ON SAID BASE STRUCTURE TO PIVOT BETWEEN SAID STATIONARY CONTACTS ABOUT AN AXIS SITUATED SUBSTANTIALLY AT THE CENTER OF CURVATURE OF SAID ARCUATE PATH, SAID CONTACT ARM HAVING A PAIR OF CONTACT SURFACE AREAS ON OPPOSITE SIDES OF SAID CONTACT ARM, THE PLANES OF WHICH ARE ARRANGED SUBSTANTIALLY NON-PERPENDICULARLY TO THE PLANE OF SAID ARCUATE PATH; AND ELECTROMAGNET MEANS MOUNTED ON SAID BASE STRUCTURE IN DRIVING RELATIONSHIP TO SAID ARM TO PIVOT SAID FLEXIBLE CONTACT ARM AND URGE ONE OF SAID CONTACT SURFACE AREAS OF SAID CONTACT ARM AGAINST THE CONTACT SURFACE AREA OF ONE OF SAID STATIONARY CONTACTS. 